Automatic reclosing circuit breaker



Nov. 30, 1948. w. D. KYLE, JR, ETAL AUTOMATIC RECLOSING CIRCUIT BREAKER 3 Sheets-Sheet 1 Original Filed June 6, 1941 IIIIIIIIIIIIIIIIIIIIIIII,

INVENTORS Mil/7M 0. kn: z/e. By [an Jam 0x5? Nov. 30, 1948'. .w.*D. KYLE, JR ET AL r 2,455,067 I AUTOMATIQRECLOSING CIRCUIT BREAKER s She ets-Shet 2 Original Filed June 6 1941 111111111111 "Ii I,

147' f ORA/f Nov. 30, 1948.

w. 0. plus, JR, ETAL AUTOMATIC RECLOSING CIRCUIT BREAKER Original Filed June 6, 1941 122W 3 22" 10M M 24; i iv) (94 K 2717; E27 25 2a 29 [74 3 Sheets-Sheet 3 INVEN TOR. ll/fllM/W 2 Km. Me. 61%! Jm/wme Patented Nov. 30, 1948 AUTOMATIC RECLOSING CIRCUIT BREAKER William 1). Kyle, Jr., Milwaukee and Carl seamsler, Wauwatosa, Wis., asslgnors to Line Material Company, a corporation of Delaware Original application June 6, 1941, Serial No. 396,850. Divided and this application July 17, 1943, Serial No. 495,118

5 Claims. 1

This invention relates to automatic reclosing circuit breakers and is a division of our application for Automatic reclosing circuit breakers, Serial No. 396,850, filed June 6, 1941.

Objects of this invention are to provide an automatic reclcsing circuit breaker in which a fully automatic reclosing circuit breaker is provided which automatically opens upon an electrical overload and automatically closes after a predetermined interval, and which is so constructed that if this opening and reclosing operation occurs a predetermined number of times in rapid succession, the circuit breaker will automatically lock itself in openposition, and in which if the opening and reclo'sing operations occur less than the predetermined number of times, the tripping mechanism will automatically reset itself so that the full predetermined number of operations in rapid succession will be required for any subsequently occurring fault.

,Further objects of this invention are to provide an automatic reclosing circuit breaker inv which the lock-out mechanism is so arranged as to permanently bias the circuit breaker in open position when the look-out mechanism operates, which i not dependent upon any pawl, ratchet, or other type of latch which might Jar loose if the circuit breaker were subjected to vibration or jarring, or which, when defective for. any cause, would allow the circuit breaker to drop closed, .but instead in which the circuit breaker when locked out is biased towards open position and remains in open position irrespective of any jarring or other disturbance that might occur, thereby providing a high factor oi safety.

Further objects are to provide an automatic repeating circuit breaker in which manual means are provided for tripping the circuit breaker upon manual operation and for resetting the circuit breaker after it has been locked out, in which this manual resetting means is so made that the circuit breaker can operate independently of such manual resetting means if the fault still persists while the circuit breaker is being manually reset, to thereby guard against any severe mechanical blows or shocks being imparted to the operator when he is resetting the circuit breaker.

Further-objects are to provide an automatic reclosing circuit breaker which not only may be opened by an electrical overload or manually, but also which is so constructed that it will be opened upon the heating beyond a predetermined temperature of the oil in which the circuit breaker is immersed so that when an overload occurs which would heat the circuit breaker but of a value insuflicient to cause operation of the circuit breaker, there can be no danger of the burning out of the circuit breaker, but in which automatic opening occurs upon a rise in temperature or the oil beyond a predetermined value. In other words, further objects are to provide a circuit breaker in which the heating of the electromagnet is utilized to cause opening of the circuit breaker by so-called "sneak currents" or currents of lesser value than that required for the electromagnetic operation of the circuit breaker.

Further objects are to provide an automatic reclosing circuit breaker in which it is not necessary to use an insulating housing but in which a metal can or housing is provided which is completed by a metal cap, all exposed parts of the apparatus being electrically dead at all times except for two terminal members which are carried by the cap and project from the upper side of the cap, the can being free from any holes or apertures or bushings therethrough and being open only at the top to thereby guard against loss of oil.

Further objects are to provide a reclosing circuit breaker in which all parts of the circuit breaker are carried from a top metal cap, the metal cap being clamped to a metal can containing oil, the construction being such that the circuit breaker may be lifted from the can, if desired, for inspection or repair without removing the can from its mounting, thus facilitating periodic inspection or repair without the necessity of removing the can from the pole or other support upon which it may be mounted, the metal can itself also providing for rapid heat dissipation.

Further objects are to provide an automatic reclosing circuit breaker which cannot be manually held in closed position against an electrical overload, which has a quick break and aquick make no matter in what manner it may be operated, whether by electrical overload, manually or by the heating of the oil, and in which the rapidly moving parts of the circuit breaker are hydraulically cushioned.

An embodiment of the invention is shown in the accompanying drawings, in which:

Figure 1 is a side' elevation, partly broken away, of the automatic repeating circuit breaker.

Figure 2 is an enlarged sectional view on the line 2-2 of Figure 1, such view also corresponding to a section on the line 2-2 of Figure 3.

Figure 3 is a sectional view on the line 33 of Figure 2.

Figure! is-a fragmentary view on'the line 4-4 of Figure 8.

Figure 5 is a view of the top plate and associated parts with the upper portion or the apparatus sectioned oil.

Figure 8 is a sectional detail of the thermostatic means, such view being taken on the line 8-8 of Figure 5.

Figure 7 is a fragmentary sectional view on the line 1-1 of Figure 2. K

Figure 8 is a sectional detail oil the time delay means.

Figure 9 is a detail showing the manual trip and reset mechanism.

Fig. 10 is a sectional view on the slanting line |8-||| of Figure 4.

Figure 11 is a fragmentary sectional view on the .line of Figure 3.

The circuit breaker is oil immersed and is mounted within the oil containing metal can i which is provided with a removable top 2 removably held to the can in any suitable manner.

Aconvenient way of attaching the top to the can is by means of a plurality of bolts 8 which are pivotally mounted between spaced ears 4 carried by the can and which are provided with wing nuts I. The wing nuts are adapted to bear against L-shaped clamping plates 8 whose downwardly extending portion is adapted to rest upon the upper face or the ears 4, a suitable lug i being provided on each of the ears to prevent the clamping plates 6 from sliding oi! the upper surface of the ears 4. A suitable sealing gasket is positioned between the flanged upper end of the can and the annular recessed portion of the cover 2, as shown most clearly in Figure 2.

Any suitable attaching means as indicated at 8 and 8 are provided on the can so that the can may be attached to a pole or other suitable support.

The cap or cover 2 is provided with a line and load terminal indicated respectively at W and ii, and these terminals are carried by insulating bushings l2, l2.

The automatic reclosing circuit breaker is sus pended in its entirety from the metal cover 2. For example, the metal cover may be provided with a plurality of downwardly extending insulating posts i3 which are secured at their upper ends to the metal cover and which have internally threaded lower portions into which elongated attaching screws l4 pass. These attaching screws hold the upper metal plate 65 and the lower metal plate i8 and the lower insulating annular block or collar il in place, the metal plates I6 and i8 being spaced apart by suitable spacers i8 which may be insulating tubes if so desired. The electromagnetic coil or solenoid i9 is positioned between the plates, suitable insulating end pieces being provided, as shown in Figure 2. Centrally oi the coil an insulating sleeve or tube 28 is provided.

A non-magnetic operating rod 2| for the circuit breaker extends upwardly centrally of the insulating tube 28 and on this rod a plunger 22 formed of magnetic material is freely slidabie. This plunger 22 or armature is provided with an enlarged or shouldered lower portion 28 which acts as a piston when passing within the cylindrical chamber 24 formed in the collar or block IT.

The operating rod 2| oi the circuit breaker rigidly carries a spider like stop 25 which loosely fits within the sleeve 28 and which serves as an abutment against which the upper end of the magnetic plunger 22 strikes when the coil i9 is energized by an overload current. When this occurs, the plunger 22 is suddenly drawn upwardiy into the coil and strikes the abutment 28, carrying the rod 2| upwardly.

The lower end of the rod 2| is rigidly secured to an insulating cross-head 28, see Figure 7. The cross-head 28 carries a pair of contact rods 21 to which are rigidly attached a pair of contact sleeves 28, see Figure 7. The contact sleeves 28 normally engage the stationary contact pins 29. These stationary contacts or contact pins 29 are connected to the line and load terminals I0 and II hereinbeiore described. The contact members 21 are connected to opposite sides 01 the coil It by means of flexible conductors 8D to thus place the coil in series in the circuit through the circuit breaker. It is to be noted from Figure 2 that arcing contacts 9| are also provided. Our copending application Serial No. 495,682, filed July 22, 1943, now Patent No. 2,414,956, issued January 28, 1947, for Automatic reclosing circuit breakers is directed to this contact construction.

Referring to Figures 2 and 3, it will be seen that a rock shaft 322 extends transversely of the cover or cap 2. A rocking sleeve 38 is loosely mounted on this rockshait and is provided with a relatively long arm 34 and a relatively shorter arm 35 which constitute, together with the sleeve 83, a unitary member freely rockabie upon the shaft 82. The relatively long arm 84 is connected by means of a pair of insulating links 38 with the upper end of the operating rod 2| of the circuit breaker, as shownmost clearly in Figure 2, Thus when the circuit breaker is driven to open position upon the occurrence of an overload, the arm 34 and the arm 88 are rocked upwardly. The arm 85 is connected by means of insulating links 8'! with a plunger 88 which is normally positioned within the relatively large portion 39 of the bore of a cylinder 48, see Figure 8.

The cylinder is provided with a relatively smaller upper bore 4| within which a spider like guiding member 42 of the plunger 38 rides. When the arms 84 and 88 are rocked upwardly. the plunger 88 passes from the relatively large bore 38 into the relatively small bore 4|. However, it is freely drawn upwardly in the relatively small bore 4i as the spring pressed valve 43 yields and allows oil to pass downwardly through apertures 44 into the space below the plunger and no material retardation occurs, thereby allowing the circuit breaker to open with a very quick stroke.

However, after the circuit breaker has opened, it cannot immediately close for there is a time delay produced by the downward travel of the plunger 38 through the relatively small bore or constricted bore 4|, the oil leaking out around the sides or the plunger 38 and retarding the downward motion of the circuit breaker. However, as the circuit breaker approaches closed position, the

plunger 38 rides out of the constructed passage 4| into the larger passage 38 of the cylinder 48 and the circuit breaker completes its closing stroke with a quick motion.

It is of course obvious that a small passage could be provided beneath the piston 38 through the wall 01' the cylinder or else through the piston itself to provide for the escape of oil or, as stated hereinabove, the oil may leak around between the piston and the cylinder. Thus a predetermined time delay is imposed upon the circuit breaker after it has opened to thereby provide an interval of time before it will close so that if the fault is only a temporary fault, the circuit breaker will stay closed after it has once opened. It the fault persists, it is obvious that the circuit breaker will again make a quick opening stroke and will also be retarded on its closing stroke.

It is desirable to provide means for permanently locking the circuit breaker in open position after a predetermined number of rapidly succeeding operations.- This is readily accomplished by providing a tripping means actuated by oil pumped by the circuit breaker upon operation. As shown in Figure 2, the collar or head I! is provided with a cylinder like aperture 24 within which the piston or enlarged shouldered portion 23 of the plunger 22 passes during the completion of the upward stroke of the plunger. This also provides a hydraulic cushion for the plunger and thus materially reduces wear. The oil from the chamber 24 passes through a port past a check valve 46 into the lower end of the cylinder 41, see Figure 2.

A piston 48 is positioned within this cylinder and is moved up a predetermined distance on each opening stroke of the plunger 22. The check valve seats and prevents the return of the oil from the bottom of the cylinder. The piston or head 23 of the plunger 22 freely passes from the cylinder 24 asa relief check valve 49 is provided to allow oil to pass back into the cylinder 24 above the piston 23.

It is obvious that after a certain number of operations, the piston 48 of the tripping device will move upwardly a suillcient distance to project the pin 50 carried thereby through an opening 5| in the top plate I5 and against the trip latch 52, thereby raising the trip latch. This raising of the trip latch, as will be described hereinafter, releases the lock-out mechanism and locks the circuit breaker in open position. However, it is desirable to have this lockout of the circuit breaker occur not only when there has been a predetermined number of operations of the circuit breaker, but also only when these operations occur in rapid succession.

If, for the purpose of illustration, it is assumed that the circuit breaker is to lock open after three operations in quick succession, it obviously is not desirable for the circuit breaker to lock open after two operations occurring in quick succession and a third operation occurring at a very much later time. This result is accomplished by providing an adjustable leak. not shown, from the cylinder 41 at a point beneath the piston 48. The

features of this last described structure are set forth and claimed in our copending application hereinabove identified of which this is a division. If, for example, less than the predetermined number of quickly succeeding operations has'occurred, the piston 48 will settle downwardly as the oil flows through the leak passage and willfinally come to rest at the bottom part of its stroke, as shown in Figure 2, thereby resetting the tripping mechanism to its initial position.

This feature is of particular importance for if the circuit breaker performs one or twooperations and the fault clears, the circuit breaker still will have its full number of times for a sequential rapid operation in the event any subsequent fault occurs.

Returning to the latching and tripping mechanism with particular reference to Figures 2 and 4, it will be seen that the latching lever is provided with a latching portion 53 beneath which a latching plate 54 is normally held, the latching late 54 being of metal and being carried by an insulating lever 55. The lever 55 is rigidly bolted to a metal lever 56, which latter is rigid with a sleeve 51. A second lever 58 is also rigid with the sleeve 51 and is spring urged in a counterclockwise direction by means of a spring 59. This spring 59 has its upper end attached at a fixed point within the cap 2, as shown in Figure 2. Therefore, it will be seen that the latch lever 55 is permanently biased towards its uppermost position which will be shown as the description proceeds to be the lock-out position for the circuit breaker.

The lever 55, as will be seen from Figures 2 and 3, is provided with a head or pin 60 positioned directly beneath the lever 34, which latter lever is attached by means of the links 35 with the operating rod 2| of the circuit breaker. Therefore it is apparent that when the trip latch 52 is released, that the circuit breaker will be locked open as the spring 59 will cause the lever 56 with the projection 60 to rock in a counterclockwise direction, see Figure 2, and thus hold the circuit breaker locked open. The circuit breaker will thus be permanently biased towards open position when it is locked out and will not be dependent upon any pawl or any other type of latch of this order which might Jar loose and allow the circuit breaker to drop to closed position.

This contingency is avoided by providing the mechanism hereinabove described which permanently biases the circuit breaker towards open position when the circuit breaker is locked open so that there is no tendency of the circuit breaker to close under these conditions although it may be subjected to vibration or jarring.

It sometimes happens that sufficient current is passed through the coil [9 to abnormally heat the coil with consequent damage to the apparatus without causing operation of the circuit breaker. These currents are frequently called sneak currents. This is prevented by providing thermal means responsive to the temperature of the oil within the tank i for operating the trip latch 52. As may be seen from reference to Figures 3, 5 and 6, a bimetallic folded strip Si is carried by the upper plate l5 and has its free end positioned beneath the trip latch 52 so that when the bimetallic strip 6! opens up as the oil becomes abnormally heated, it will raise the trip latch 52 and release the trip lever 55, thereby causing a quick opening of the circuit breaker under the influence of the spring 59 and lock-out of the circuit breaker. It will be seen that the heating of the coil i9 is taken advantage of, and the circuit breaker is thus protected against the.

sneak currents.

Manual means are also provided for opening the circuit breaker with a quick opening stroke. The manual operating means consists of an eyeleted lever 62, see Figures 3 and 9, which is positioned within a hood 63 integral with the cap 2. The hood is open at its lower side and is provided with a cut out portion 64 so that the hook of a switch stick may be inserted in the eye of the lever 62 and the lever may be drawn downwardly to cause a quick opening of the circuit breaker in a manner hereinafter to appear, or to move the lever upwardly back to the position shown in Figure 9 to reset the circuit breaker.

The lever 62 is rigidly attached to the shaft 32 and the shaft 32 rigidly carries a reset lever 65 and an eccentric 66. The eccentric 65 is shown most clearly in Figures 3 and 4. The sleeve 51, see Figures 3 and 4, is loosely mounted on the eccentric 66 and is free to rock about such eccentric independently of any action of the occentric. However, when the lever 62 is pulled aaeaocv 7 downwardly, the eccentric 6t draws the latch lever 55 upwardly in a slanting direction towards the left as viewed in Figure 4i, and thus withdraws the latch plate 54 from the latch portion 58 oi the latch lever 62. The spring b9 is now free to act and causes a quick counterclockwise stroke of the lever 55 whose pin or projecting portion til strikes the lever at and opens the circuit breaker with a quick opening stroke. The circuit breaker will now be permanently locked open until it is manually reset.

The resetting is accomplished through the me dium of the lever 62, the shaft lit and the reset lever 65, see Figures 3, i and. ill. The reset lever 65 is positioned above a pin or projection 61 rigid with the latching lever Elli, as shown most clearly in Figure 10, the projection ill being shown in dotted lines in Figure 3. It is clear that when the lever $2 is rocked in a clockwise direction back to its position shown in Figure 9, that the reset lever til will engage the pin El and will force the latching lever lib downwardly against the action of the spring til to its normal position as shown in Figure 2, thus resetting the circuit breaker. The circuit breaker will thereafter close after a suitable interval determined by the time delay mechanism shown in Figure a and herein above described.

It is to be noted that a relatively light spring 68 is secured to the reset lever to and to a pin 69 carried by the lever 58. The spring till is rela tively light as compared to the spring b9 and serves merely to hold the lever t2, see Figures 3 and 9, in its uppermost position until the lever 62 has been rocked downwardly when the circuit breaker is locked out.

It is to be noted that the lever [it does not move downwardly for each operation oi the cir-= cult breaker but only moves downwardly when the lock-out mechanism functions or when the lever 62 is manually pulled downwardly for manual operation of the circuit breaker.

It is to be noted particularly that in the resetting operation, the lineman or operator is never subjected to any violent shock even though the fault may still persist when the circuit breaker is reset. When the circuit breaker is reset and the fault still persists, the circuit breaker will instantly move to full open position but nevertheless the lever 34, see'Figure 2, will move upwardly away from the projection 8d of the lever 56 and consequently no blow or jar will be imparted to the operator. The only force opposing the resetting is the spring 68 and the force due to the opening stroke of the circuit breaker is not imparted to the resetting and manual release I lever 62.

Another feature to be noted is that in the event the circuit breaker is closed. and it is desired to manually open it, no matter how slowly the oper== ator pulls downwardly on the lever 62 by means oi a switch stick, for instance, as soon as the latch lever 55, see Figure 2, is withdrawn from the latch member 52, the circuit breaker will execute a quick opening stroke due to the action of the spring 69 hereinbeiore described.

Thus the circuit breaker always has a quick opening stroke no matter whether it is released manually, thermally, or by electrical overload. It also has a quick closing stroke after a certain interval provided by the time delay mechanism as the final closing stroke of the circuit breaker is unimpeded as hereinabove described.

It is preferable to encase the lower portion of the circuit breaker, that is to say, the stationary and movable contacts, within an insulating cylindrical sleeve 10. The upper end of the sleeve ill is closed, except for the passageways hereinbefore described, by means of the collar or member i! and the lower end of the sleeve in is closed by means of the base member ll. This base memher is provided with an oil inlet aperture 12, see Figure 2, which is normally closed by a downwardly seating flap valve iii.

As will be seen from Figure 1, theinsulating base member ll is suspended by means of the insulating rods M. These rods extend upwardly to the portion ill and are internally threaded at their upper and lower ends to receive bolts to thereby lock the rods in place and to the base ii. The insulating sleeve or shell it is therefore clamped between the insulating head or collar ii and the insulating base l Ii.

It is preferable to provide insulating partitions extending upwardly between the spaced contacts. These partitions may take the form of two members lb of insulating material which have integrally formed, outwardly bent foot portions 76, see Figure 7. The foot portions are clamped in place by the stationary contacts.

By having the base or foot portions it of the members in integral with the vertical portions thereof, it is apparent that any conducting sediment that may settle downwardly between the stationary contacts will not form a bridge path from one contact to the other. Further, in view of the fact that the members it and iii are integral, it is apparent that no conducting sediment can form and lead up to a short gap across which the arc would strike.

By having the lower portion or active contacts of the circuit breaker enclosed by the sleeve ill and base portion "ii and upper collar or member ill, see Figure 2, it is apparent that under violent overload where a considerable amount of gas is generated, that the tripping plunger 48 will be driven to its uppermost position and will trip the look-out mechanism and thereby lock the circuit breaker in open position so that a succeeding violent action of the circuit breaker will not be permitted even if the fault persists.

This is a very unusual condition but the constructlon of this device is such that it will care for this abnormal condition and will save the circuit breaker from the necessity of executing the required number of operations in rapid sequence under an extremely heavy abnormal overload.

This invention is designed to take care of still another abnormal condition where an overload of too small a value occurs to cause complete operation of the circuit breaker at one stroke, but nevertheless might cause a partial opening followed by quick reclosing of the circuit breaker without having the circuit breaker execute a complete opening stroke. It is obvious that the repeated breaking will result in the generation of gas and the gas so generated will force oil into the cylinder 41, thereby driving the tripping plunger 48 upwardly, thus tripping the lock-out mechanism.

Although this invention has been described in considerable detail, it is to be understood that such descrlption'is intended as illustrative rather than limiting, as the invention may be variously normally biased closed, normally ineffective lockout means for locking said contact 'means open, counting means responsive to a number of successive operations of said circuit breaker occurring in rapid succession for rendering said lockout means efiective, a liquid dielectric surrounding said electromagnetic means and said contact means and arranged to be heated by said electromagnetic means, and temperature responsive means submerged in said liquid dielectric and responsive to the temperature thereof for rendering said lockout means efiective irrespective of the position of said counting means, whereby said electromagnetic means is protected from heat generated as a result of current through said circuit breaker which current is insufiicient to actuate said electromagnetic means.

2. In a device of the class described, contact means normally biased closed, normally restrained lockout means permanently biased towards lockout position for moving said contact means to open position and for locking said contact means in open position, an electromagnet controlled by said contact means and arranged to open said contact means on overload exceeding a predetermined current value and arranged to act as a heating means, and thermostatic means responsive to the temperature of said electromagnet and arranged to release said lockout means for current of lesser value than that means normally biased closed, normally restrained lockout means permanently'biased towards lockout position for moving said contact means to open position and for locking said contactmeans in open position, an electromagnet controlled by said contact means and arranged to open said contact means on overload exceeding a predetermined current value and arranged to act as heating means, a liquid dielectric surrounding said electromagnet and said contact means and arranged to'be heated by said electromagnet, and thermostatic means submerged in said dielectric and arranged to release said lockout means when said dielectric has arrived at a predetermined temperature due to heating of said electromagnet by currents above a predetermined value but of a lesser value than said first mentioned predetermined value.

4. In a device of the class described, contact means normally biased towards closed position, normally inactive lockout means permanently biased towards lockout position'ior moving said contact means to open position and for locking said contact means in open position, latch means arranged to hold said lockout means in its normally inactive position, an elcctromagnet con-- trolled by said contact means and arranged to open said contact means on overload, a liquid dielectric surrounding said electromagnet and said contact means, and a bimetal member submerged in said liquid dielectric and responsive to the temperature of said liquid dielectric and positioned in operative relation to said latch means and arranged to operate said latch means to thereby release said lockout means when said liquid dielectric is heated by said electromagnet by overload current above a predetermined value but less than that required to electromagnetically operate said contact means.

5. An automatic reclosing circuit breaker comprising contact means, electromagnetic means responsive to an electrical overload for opening said contact means, said contact means being normally biased closed, normally ineffective lockout means for locking said contact means open,

latch means arranged to release said lockout means and normally holding said lockout means in ineffective position, counting means responsive to a number of successive operations of said circuit breaker occurring in rapid succession for rendering said lockout means effective, a liquid dielectric surrounding said electromagnetic means and said contact means and arranged to be heated by said electromagnetic means, a bimetal member submerged in said liquid dielectric and arranged to operate said latch to release said lockout means for currents above a predetermined value but less than that required to electromagnetically operate said circuit breaker.

WILLIAM D. KYLE, Ja. CARL SCHINDLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 433,022 Noyes July 29, 1890 508,652 Thomson Nov. 14, 1893 707,967 Griscom Aug. 26, 1902 1,214,771 Fortier Feb. 6, 1917 1,289,649 De Camp Dec. 31, 1918 1,530,730 Leeb Mar. 24, 1925 1,629,640 Schachtner May 24, 1927 1,732,295 Aichele Oct. 22, 1929' 2,091,035 Foster Aug. 24, 1937 2,242,066 Grady May 13, 1941 2,321,603 Jensen June 15, 1943 2,333,604 Wallace Nov. 2, 1943 FOREIGN PATENTS Number Country Date 475,870 Germany my 4, 1929 

